The invention generally relates to hydraulic servo valves and specifically to a pilot-operated servo valve with four main- stream ports for mounting into a control block.
Pilot-operated electrohydraulic servo valves of twin- and multi-stage design with four main-stream ports are used as 4-way valves to control the position, speed and force in cylinders for linear movements or position, rotational speed and torque in hydraulic motors for rotary movements.
They are conventionally designed as plate-stack valves, i.e. they have a prismatic valve housing for mounting on a connection surface of a hydraulic block. The four main-stream ports of the valve lie in a planar connection surface of the valve housing, and their openings into the control bore of a main control piston are designed symmetrically. Control chambers are arranged in end caps flange-mounted on the valve housing on both sides. These control chambers are connected via control bores to a pilot servo valve. The symmetrical main control piston is hydraulically actuated by applying pressure to its two end surfaces in the end control chambers. Pilot-operated 4-way servo valves with valve housing for mounting on a connection surface of a hydraulic block are highly space-consuming and require complicated bores in the hydraulic block for the four main-stream ports.
Prior art pilot-operated 4-way servo valves have a spring-centered rest position. In most cases the main control piston is centered via two opposite return springs arranged in the end control chambers and acting against each other.
A pilot-operated 4-way proportional valve with one-sided spring centering is described in the German hydraulic handbook "Der Hydraulik Trainer Band 2", published by Mannesmann Rexroth GmbH, DE-8770 Lohr am Main (Germany), 3rd edition 1989, page 31, FIG. 33. The disclosed valve is conceived for mounting on a connection surface of a hydraulic block. The control chambers of the valve are disposed in end caps, which are flange-mounted on opposite sides of a valve body. DE-A-4011908 discloses a 5-way valve with one-sided spring centering and an actuating piston disposed at the opposite end of the main control piston. This valve too is conceived for mounting on a connection surface of a hydraulic block.